1. Field of the Invention
The present invention relates to an X-ray analysis apparatus in which X-rays emitted from an X-ray source are applied to a sample and a semiconductor X-ray detecting means such as a CCD (Charge Coupled Device) sensor detects the X-rays diffracted by the sample.
2. Description of the Related Art
Most X-ray analysis apparatuses have an X-ray generating unit and an X-ray detector. The X-ray generating unit applies an X-ray to a sample. The X-ray detector detects the X-ray that is emerging from the sample. In the X-ray analysis apparatus, when an X-ray is applied to a sample and the incident angle of the X-ray with respect to the sample is set to be a specific angle, the X-ray is diffracted by the sample. The diffracted X-ray emerges from the sample. The X-ray, thus diffracted, is detected by the X-ray detector.
Various types of X-ray detectors are known, such as zero-dimensional X-ray detector, one-dimensional X-ray detector, and two-dimensional X-ray detector. These X-ray detectors are also known as zero-dimensional counter, one-dimensional counter and two-dimensional counter, respectively.
The zero-dimensional X-ray detector is an X-ray detector that is configured to detect X-rays as points. Examples of zero-dimensional X-ray detectors, known in the art, are PC (Proportional Counter) and SC (Scintillation Counter). The one-dimensional X-ray detector is an X-ray detector that is configured to detect X-rays as lines. Examples of one-dimensional X-ray detectors, known in the art, are PSPC (Position Sensitive Proportional Counter) and one-dimensional CCD sensor. The PSPC has linear signal lines, each generating an electric signal at the position where an X-ray is applied. The one-dimensional CCD sensor has a plurality of CCD elements arranged in a row.
The two-dimensional X-ray detector is an X-ray detector that is configured to detect X-rays in a plane. Examples of two-dimensional X-ray detectors, known in the art, are those known as imaging plate and two-dimensional CCD sensor. The imaging plate is a detector plate that has an X-ray receiving surface coated with storage phosphor. The two-dimensional CCD sensor has a plurality of CCD (Charge Coupled Device) elements arranged in rows and columns.
The CCD sensor described above used as the one-dimensional CCD sensor or two-dimensional CCD sensor is one of semiconductor position sensors. In recent years, various X-ray analysis apparatuses have been proposed, each comprising a semiconductor position sensor such as a CCD sensor as an X-ray detector. It is expected that X-ray analysis apparatuses of this type analyze X-rays faster than the zero-dimensional counter and the one-dimensional counter.
Conventionally, there is disclosed an X-ray analysis apparatus that uses a two-dimensional CCD sensor and optical fibers to obtain a two-dimensional diffraction image whose area is broader than the two-dimensional CCD sensor in e.g. Japanese Patent Laid-Open Publication No. 2002-116158, pp. 3–6, FIG. 1. The two-dimensional diffraction image is a diffraction image that is displayed two-dimensionally or in a plane, as shown in FIG. 8. In the conventional X-ray analysis apparatus disclosed in the publication, as shown in FIG. 6, a phosphor material 102 is arranged behind a sample ‘S’ when viewed from an X-ray source 101, and the phosphor material 102 has its light-outgoing surface (that is right side surface in FIG. 6) coupled to a bundle of plural optical fibers 103 with its longitudinal cross-section formed into a taper, and the optical fibers 103 has its light-outgoing end (that is right side end in FIG. 6) coupled to a two-dimensional CCD sensor 104.
In the conventional X-ray analysis apparatus, a diffracted X-ray emerging from the sample ‘S’ is applied to the phosphor material 102 to form a light image corresponding to the diffracted X-ray in the phosphor material 102. Then the light image is directed to the two-dimensional CCD sensor 104 by the optical fibers 103, and is accumulated in plural pixels of the CCD sensor 104 as electric charges. It is expected that X-ray analysis apparatuses of this type analyze X-rays faster than the zero-dimensional counter and the one-dimensional counter.
Each of the plural optical fibers 103 used in the conventional X-ray analysis apparatus has its longitudinal cross-section tapered so that the diameter of the optical fibers 103 at the phosphor material 102 side becomes large and that at the CCD sensor 104 side becomes small. This type of CCD sensor using thus tapered optical fibers 103 is referred to as a tapered CCD sensor. Generally, the CCD sensor 104 is cooled when in use.
When employing the conventional X-ray analysis apparatus using the tapered CCD sensor shown in FIG. 6, since the light image is distorted due to distortion of the optical fibers 103 themselves, there is raised a problem that data obtained by the CCD sensor is not correct. Furthermore, since the X-ray image is once converted to light by the phosphor material 102 and thus converted data is detected by the CCD sensor, there is also raised a problem that data obtained by the CCD sensor is not correct.
On the other hand, in case of using a two-dimensional CCD sensor to obtain a two-dimensional diffraction image whose area is broader than the receiving surface of the two-dimensional CCD sensor, other than the method shown in FIG. 6, there is proposed a method in which X-rays are detected while the sample being a subject and the two-dimensional CCD sensor being an X-ray detector are moving relative to each other. However, employing this method, the X-ray analysis apparatus can hardly detect X-rays at high speed and high sensitivity. This is because the spatial resolution of the conventional CCD sensor is approximately 100 μm at most, and the plural CCD pixels cannot obtain data or an image at high resolution when the sample and the two-dimensional CCD sensor move relative to each other at an excessively high speed.